Method to Control a Burner for an Exhaust System of an Internal Combustion Engine

ABSTRACT

A method to control an internal combustion engine having an exhaust duct and an exhaust gas after-treatment system comprising at least one catalytic converter arranged along the exhaust duct; an oxygen sensor housed along the exhaust duct and arranged upstream of said at least one catalytic converter; and a burner suited to introduce the exhaust gases into the exhaust duct upstream of the oxygen sensor the method provides the steps of calculating the thermal power required to reach the nominal operating temperature of said at least one catalytic converter obtained with an objective value of the air/fuel ratio value; and determining both the objective fuel flow rate and the objective air flow rate to be fed to the burner to obtain the thermal power required to reach the nominal operating temperature of said at least one catalytic converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102021000017255 filed on Jun. 30, 2021, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method to control a burner for an exhaust system of an internal combustion engine.

PRIOR ART

As is known, an internal combustion engine is typically provided with a number of cylinders, each of which is connected to an intake manifold and an exhaust manifold, to which an exhaust duct is connected which feeds the exhaust gases produced by combustion to an exhaust system, which emits the gases produced by combustion into the atmosphere.

An exhaust gas after-treatment system usually comprises a precatalytic converter arranged along the exhaust duct; a particulate filter also arranged along the exhaust duct, downstream of the precatalytic converter; and a catalytic converter arranged along the exhaust duct, upstream of the particulate filter.

Also provided along the exhaust duct are a first lambda sensor housed along the exhaust duct and arranged upstream of the precatalytic converter to detect the air/fuel ratio (or titer) of the exhaust gases entering the precatalytic converter; a second lambda sensor housed along the exhaust duct and interposed between the precatalytic converter and the assembly defined by the catalytic converter and by the particulate filter to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter; and lastly, a third lambda sensor housed along the exhaust duct and arranged downstream of the assembly defined by the catalytic converter and by the particulate filter to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter and by the particulate filter.

Lastly, the exhaust gas after-treatment system also comprises a burner suited to introduce the exhaust gases (and consequently heat) into the exhaust duct so as to speed up heating of the catalytic converter and so as to facilitate the regeneration of the particulate filter.

A combustion chamber is defined inside the burner, the chamber receives fresh air and receives fuel from an injector, which is designed to cyclically inject fuel inside the combustion chamber. In addition, a spark plug is coupled to the burner to determine the ignition of the mixture present inside the combustion chamber.

It is of utmost importance to be able to control the combustion that occurs inside the burner so as to ensure that the optimal thermal power and the desired/objective value of the air/fuel ratio of the exhaust gases exiting the burner are achieved.

For this reason, it has been proposed to house a further lambda sensor along a duct adapted to discharge the exhaust gases exiting the burner into the exhaust duct; said further lambda sensor is dedicated exclusively to detecting the air/fuel ratio of the exhaust gases exiting the burner. However, this solution is economically disadvantageous as it involves the use of a further lambda sensor.

To overcome this problem, it has been proposed to arrange the burner so as to introduce the exhaust gases into the exhaust duct between the first lambda sensor (so that the first lambda sensor is exclusively hit by the exhaust gases produced by the internal combustion engine) and the second lambda sensor (so that the second lambda sensor is hit by both the exhaust gases produced by the internal combustion engine and the exhaust gases produced by the burner); and use the signals coming from the first lambda sensor and from the second lambda sensor to control the burner and operate the air flow rate and fuel fed to the burner.

The document US2007157606 relates to a method to control a burner for an exhaust system of an internal combustion engine.

DESCRIPTION OF THE INVENTION

The aim of the present invention is to provide a method to control a burner for an exhaust system of an internal combustion engine which is free of the drawbacks described above and, in particular, is easy and inexpensive to implement.

According to the present invention, a method to control a burner for an exhaust system of an internal combustion engine is provided according to what is claimed in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the appended drawings, which illustrate a non-limiting embodiment thereof, wherein:

FIG. 1 schematically shows an internal combustion engine provided with a first variant of an exhaust gas after-treatment system having an electronic control unit that implements the control method obtained in accordance with the present invention;

FIG. 2 illustrates a second variant of the exhaust gas after-treatment system of FIG. 1 ;

FIG. 3 schematically illustrates a detail of the exhaust gas after-treatment system illustrated in FIGS. 1 and 2 ;

FIGS. 4 and 6 are block diagrams that schematically illustrate a first variant of the method to control the air flow rate object of the present invention;

FIG. 5 is a block diagram that schematically illustrates the method to control the fuel flow rate object of the present invention;

FIGS. 7 and 8 are block diagrams that schematically illustrate a second variant of the method to control the air flow rate object of the present invention;

FIGS. 9 and 10 are block diagrams that schematically illustrate a third variant of the method to control the air flow rate object of the present invention;

FIGS. 11 and 12 are block diagrams that schematically illustrate a fourth variant of the method to control the air flow object of the present invention; and

FIG. 13 schematically illustrates a detail of the internal combustion engine of FIG. 1 ; and

FIG. 14 schematically illustrates a further embodiment of a detail of FIG. 3 .

PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1 , indicated as a whole by the number 1 is a boosted internal combustion engine provided with an exhaust system 2 for the exhaust gases in a motor vehicle (not illustrated) and having a number of cylinders 3, each of which is connected to an intake manifold 4 and to an exhaust manifold 5 by at least one respective exhaust valve (not illustrated).

Also, according to a preferred embodiment, the following disclosure finds advantageous yet not exclusive application in the case of an internal combustion engine 1 in which the fuel fed is gasoline.

The intake manifold 4 receives air coming from the external environment through an intake duct 6, which is provided with an air filter 7 for the flow of fresh air and is regulated by a throttle valve 8. A mass air flow sensor 9 (better known as Air Flow Meter) is also arranged along the intake duct 6 downstream of the air filter 7.

The exhaust manifold 5 is connected to an exhaust duct 10 that feeds the exhaust gases produced by combustion to the exhaust system 2, which emits the gases produced by combustion into the atmosphere.

The boosting system of the internal combustion engine 1 comprises a turbocompressor 11 provided with a turbine 12, which is arranged along the exhaust duct 10 to rotate at high speed under the action of the exhaust gases expelled from the cylinders 3, and a compressor 13, which is arranged along the intake duct 6 and is mechanically connected to the turbine 12 to be dragged into rotation by said turbine 12 so as to increase the pressure of the air present in the intake duct 6.

The gas exhaust system 2 is provided with an exhaust gas after-treatment system 14 comprising a precatalytic converter 15 arranged along the exhaust duct 10, downstream of the turbocompressor 11 and a particulate filter 16 (also known as Gasoline Particulate Filter) also arranged along the exhaust duct 10, downstream of the precatalytic converter. According to a preferred embodiment, the exhaust after-treatment system 14 is provided with a catalytic converter 17 arranged along the exhaust duct 10, upstream of the particulate filter 16. According to a preferred embodiment, the catalytic converter 17 and the particulate filter 16 are arranged one after the other inside a common tubular container.

According to a first variant, the internal combustion engine 1 is also provided with a linear oxygen sensor 18 of the UHEGO or UEGO type housed along the exhaust duct 10 and interposed between the turbocompressor 11 and the precatalytic converter 15 so as to detect the air/fuel ratio (or titer) of the exhaust gases (providing a linear output indicating the content of oxygen in the exhaust gases) downstream of the turbocompressor 11 and upstream of the precatalytic converter 15.

The internal combustion engine is also provided with a lambda sensor 19 intended to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct 10 and interposed between the precatalytic converter 15 and the assembly defined by the catalytic converter 17 and by the particulate filter 16 to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter 15; and finally, a lambda sensor 20 suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct and arranged downstream of the assembly defined by the catalytic converter 17 and by the particulate filter 16 to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter 17 and the particulate filter 16.

According to a second variant illustrated in FIG. 2 , the internal combustion engine 1 is also provided with a lambda sensor 19* suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct 10 and interposed between the turbocompressor 11 and the precatalytic converter 15 to detect the air/fuel ratio (or titer) of the exhaust gases downstream of the turbocompressor 11 and upstream of the precatalytic converter 15.

The internal combustion engine 1 is also provided with a UHEGO or UEGO type linear oxygen sensor 18* housed along the exhaust duct 10 and interposed between the precatalytic converter 15 and the assembly defined by the catalytic converter 17 and by the particulate filter 16 to detect the oxygen concentration inside the exhaust gases downstream of the precatalytic converter 15 (a linear output indicating the content of oxygen in the exhaust gases); and lastly, a lambda sensor 20 suited to provide a binary on/off type output indicating whether the exhaust gases titer is above or below the stoichiometric value, housed along the exhaust duct 10 and arranged downstream of the assembly defined by the catalytic converter 17 and by the particulate filter 16 to detect the oxygen concentration inside the exhaust gases downstream of the assembly defined by the catalytic converter 17 and by the particulate filter 16.

The exhaust gas after-treatment system 14 then comprises a burner 21 suited to introduce exhaust gases (and consequently heat) into the exhaust duct 10 so as to speed up the heating of the precatalytic converter 15 and/or of the catalytic converter 17 and so as to facilitate the regeneration of the particulate filter 16.

According to what is better illustrated in FIG. 3 , a combustion chamber 22 is defined inside the burner 21, the chamber receives fresh air (i.e., air coming from the outside environment) through an air feeding circuit 23 provided with a pumping device 24 that feeds the air by means of a duct 25 regulated by an on/off type shut-off valve 26. The combustion chamber 22 also receives fuel from an injector 27 designed to cyclically inject fuel inside the combustion chamber 22. In addition, a spark plug 28 is coupled to the burner 21 to determine the ignition of the mixture present inside said combustion chamber 22. The internal combustion engine 1 then comprises a fuel feeding circuit 29 provided with a pumping device 30 that feeds the fuel by means of a duct 31.

Lastly, the internal combustion engine 1 comprises a control system 32 which is adapted to oversee the operation of said internal combustion engine 1. The control system 32 comprises at least one electronic control unit (normally referred to as an “ECU”—“Electronic Control Unit”), which oversees the operation of the various components of the internal combustion engine 1.

The spark plug 28 is operated by the electronic control unit ECU to make a spark between its electrodes and therefore determine the ignition of the gases compressed inside the combustion chamber 22. The control system 32 also comprises a plurality of sensors connected to the electronic control unit ECU.

The sensors comprise, in particular, a sensor 33 for the temperature and pressure of the air flow fed to the burner 21 preferably housed along the duct 25; a sensor 34 for the temperature and pressure of the exhaust gases exiting the burner 21 housed along an outlet duct 35 for discharging the exhaust gases exiting the burner 21 into the exhaust duct 10; a sensor 36 for the pressure of fuel fed to the burner 21 housed along the duct 31; and a sensor 37 for the pressure and temperature of the air flow fed to the pumping device 24.

The electronic control unit ECU is also connected to the UHEGO or UEGO type linear oxygen sensor 18, 18* and to the lambda sensors 19, 19*, 20.

According to a first embodiment illustrated in FIG. 1 , the burner 21 is arranged so as to introduce the exhaust gases into the exhaust duct 10 upstream of the UHEGO or UEGO type linear oxygen sensor 18 and upstream of the precatalytic converter 15.

According to a second embodiment illustrated in FIG. 2 , the burner 21 is arranged so as to introduce the exhaust gases into the exhaust duct 10 upstream of the UHEGO or UEGO type linear oxygen sensor 18* and upstream of the assembly defined by the catalytic converter 17 and by the particulate filter 16.

The method implemented by the electronic control unit ECU to control the burner 21 is described in the following.

Firstly, the strategy described in the following disclosure may be implemented exclusively when the UHEGO or UEGO type linear oxygen sensor 18, 18* is hit exclusively by the exhaust gases produced by the burner 21 (in other words, it is necessary that the UHEGO or UEGO type linear oxygen sensor 18, 18* is not hit by the exhaust gases produced by the internal combustion engine 1).

Therefore, the condition of enabling the control strategy for the burner 21 is that said burner 21 is turned on and the internal combustion engine 1 is instead turned off.

In particular, the following two conditions may occur alternatively:

a) burner 21 turned on with the “cold” exhaust system 2 (i.e., with a detected temperature below a limit value, ranging from 180° C. to 200° C.); or b) burner 21 turned on with the “hot” exhaust system 2 (i.e., with a detected temperature above a limit value, ranging from 180° C. to 200° C.)

The condition a) may occur in any of the following cases:

a₁) the burner 21 is turned on when the door of the driver of the motor vehicle is opened (the opening is detected by means of a sensor or when the door is unlocked by remote control or even when the smart key is detected in proximity to the vehicle); a₂) the burner 21 is turned on when the motor vehicle is a hybrid vehicle that is started in electric mode and the internal combustion engine 1 has not been turned on yet after the motor vehicle has been started; a₃) the burner 21 is turned on when the vehicle is a hybrid vehicle running in electric mode and the electronic control unit ECU provides for switching to thermal mode (for example, in the case where the State Of Charge of a storage system is not sufficient to proceed in electric mode); in this case, the burner 21 is turned on about 3 to 5 seconds before the start of the internal combustion engine 1.

It is clear that, alternatively, in the case where the burner 21 is arranged so as to introduce the exhaust gases into the exhaust duct 10 upstream of the UHEGO or UEGO type linear oxygen sensor 18* and upstream of the assembly defined by the catalytic converter 17 and by the particulate filter 16 (in other words, in the case where the burner 21 is interposed between the precatalytic converter 15 and the assembly defined by the catalytic converter 17 and by the particulate filter 16), the strategy described in the following disclosure may also be implemented in the case where the internal combustion engine 1 is turned on since the exhaust gases produced by the internal combustion engine 1 have already passed through the precatalytic converter 15.

The burner 21 is then turned off if any of the following conditions occur:

-   -   a temperature of the exhaust system 2 above a limit value         ranging from 180° C. to 200° C. is detected; or     -   when a predetermined amount of time has elapsed since the burner         21 was turned on; or     -   in the case where the estimated energy supplied, for example, by         means of the integral of the fuel flow rate exceeds a threshold         value;     -   in the case where no passenger is detected to be present on         board the motor vehicle for a predetermined amount of time by         means of at least one recognition device housed in the passenger         compartment (such as, for example, a sensor in a seat of the         driver of the motor vehicle, or a sensor of the seat belt of the         driver of the motor vehicle).

The condition b) may, on the other hand, occur in any of the following cases:

b1) the burner 21 is turned on when the motor vehicle is a hybrid vehicle running in electric mode with the internal combustion engine 1 turned off; b2) the burner 21 is turned on during the release phase with the open clutch; and b3) the burner 21 is turned on during all the stopping phases of the motor vehicle; for example, the burner 21 is turned on during the stopping phases for a motor vehicle provided with the “Start and Stop” system, during parking manoeuvres of the motor vehicle, or even during the “after run” phase that allows the ventilation to be activated after the internal combustion engine 1 is turned off.

The burner 21 is then turned off in the case where any of the following conditions occur:

c) the internal combustion engine 1 is turned on; d) a predetermined amount of time has elapsed since the burner 21 was turned on; or e) the adaptive strategy outlined in the following disclosure has been completed.

The strategy implemented by the electronic control unit ECU to operate the burner 21 is described below.

Firstly, the electronic control unit ECU is designed to calculate the thermal power P_(OBJ) required to reach the nominal operating temperature T_(CAT_OBJ) of the precatalytic converter 15 or the catalytic converter 17 and obtained with the objective value λ_(OBJ) of the air/fuel ratio.

To calculate the thermal power P_(OBJ), it should be considered that the objective is to heat the precatalytic converter 15 or the catalytic converter 17 from an initial temperature T₀ up to the nominal operating temperature T_(CAT_OBJ); the heat Q_(CAT) required to allow this temperature increase may be calculated as follows:

Q _(CAT) =C _(CAT) *M _(CAT)*(T _(CAT_OBJ) −T ₀)

where C_(CAT) is the specific heat of the precatalytic converter 15 or the catalytic converter 17 and M_(CAT) represents the mass of the precatalytic converter 15 or the catalytic converter 17 (in essence, the product C_(CAT)*M_(CAT) represents the thermal capacity of the precatalytic converter 15 or the catalytic converter 17).

In order to heat the precatalytic converter 15 or the catalytic converter 17 in an amount of time Δt and taking into account heat losses Q_(DISS) (by convection, gases leaving the catalytic converter, etc.), the thermal capacity P_(OBJ) required is therefore given by:

P _(OBJ)=(Q _(CAT) +Q _(DISS))/Δt

The thermal power P_(t) released by the combustion in the burner 21 with an air flow {dot over (m)}_(A) and titer λ may instead be calculated as follows:

P _(t) ={dot over (m)} _(A)/λ_(ST)*[1/(MAX(1,λ)*H _(i)*η_(c)−(1/MIN(λ,1)−1)*H _(v)]

where λ_(ST) is the stoichiometric air/fuel ratio; λ is the combustion titer; {dot over (m)}_(A) is the air mass flow rate; H_(i) is the lower heating power of the fuel; H_(v) is the latent heat of vaporization of the fuel; and η_(c) is the combustion efficiency.

Therefore, once the combustion air/fuel ratio (or titer) A is defined, the air flow rate {dot over (m)}_(A) required to heat the precatalytic converter 15 or the catalytic converter 17 from an initial temperature T₀ to the nominal operating temperature T_(CAT_OBJ) may be calculated, in the case where the internal combustion engine 1 is turned off, as follows:

{dot over (m)} _(A)=(C _(CAT) *M _(CAT)*(T _(CAT_OBJ) −T ₀)+Q _(DISS))/Δt)*λ_(ST)/[1/(MAX(1,λ)*H _(i)*η_(c)−(1/MIN(λ,1)−1)*H _(v)]

In the case where the internal combustion engine 1 is turned on, the contribution due to the heat Q_(ENGINE) (positive if supplied or negative if subtracted) generated for the exchange of exhaust gases may be added as follows:

{dot over (m)} _(A)=(C _(CAT) * M _(CAT)*(T _(CAT_OBJ) −T ₀)++Q _(DISS) −Q _(ENGINE))/Δt)*λ_(ST)/[1/(MAX(1,λ)*H _(i)*η_(c)−(1/MIN(λ,1)−1)*H _(v)]

Depending on the thermal power P_(OBJ) required to reach the nominal operating temperature T_(CAT_OBJ) of the precatalytic converter 15 or of the catalytic converter 17, the electronic control unit ECU determines both the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N).

According to a first variant, the pumping device 24 is regulated by controlling the number N of revolutions while the shut-off valve 26 is of the on/off type.

The electronic control unit ECU is then designed to determine the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N), which are obtained by operating the pumping device 24, the shut-off valve 26, the pumping device 30 and the injector 27.

According to what is illustrated schematically in FIG. 4 , the objective air flow rate {dot over (m)}_(A_OBJ) is provided at input to a map (typically provided by the manufacturer of the pumping device 24) together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the nominal number N_(NOM) of revolutions with which to operate the pumping device 24.

However, the actual number N of revolutions with which to operate the pumping device 24 is defined by the sum of the nominal number N_(NOM) of revolutions and two further contributions.

In particular, the nominal number N_(NOM) of revolutions with which to operate the pumping device 24 represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N_(CL) is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution N_(ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}A and fuel flow rate {dot over (m)}_(F)).

According to what is illustrated in FIG. 6 , the third contribution N_(ADAT) with which to operate the pumping device 24 is then used to update the map used previously to determine the nominal number N_(NOM) of revolutions. In particular, the third contribution N_(ADAT) is provided at input to the map together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the updated value of the estimated air flow rate {dot over (m)}A.

In the case where the sum of the closed-loop contribution N_(CL) and of the third contribution N_(ADAT) is greater than a calibratable threshold value THR₁, a breakdown or fault is diagnosed.

According to a second variant, the pumping device 24 is not regulated by controlling the number N of revolutions while the shut-off valve 26 is produced with the variable/adjustable passage section (in other words, the shut-off valve 26 is not of the on/off type). In this case, a pressure sensor 38 is also provided in the duct 25 downstream of the shut-off valve 26 to detect the pressure of the air being fed to the burner 21.

The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N) that are obtained by operating the shut-off valve 26, the pumping device 30 and the injector 27.

According to what is illustrated schematically in FIG. 7 , the objective air flow rate {dot over (m)}_(A_OBJ) is provided at input to a map (typically provided by the manufacturer of the shut-off valve 26) together with further quantities that comprise the pressure P_(A) and the temperature T_(A) of the air provided by the sensor 33 and the pressure P_(BURN) of the air being fed to the burner 21 provided by the sensor 38. The map provides at output the nominal passage section α_(NOM) with which to operate the shut-off valve 26.

The actual passage section α_(OBJ) with which to operate the shut-off valve 26 is, however, defined by the sum of the nominal passage section α_(NOM) and two further contributions.

In particular, the nominal passage section α_(NOM) with which to operate the shut-off valve 26 represents the open-loop contribution and is precisely generated using the experimentally derived control map. In the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air is less than or equal to a threshold value THR, the closed-loop contribution α_(CL) is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value A of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution α_(ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}A and fuel flow rate {dot over (m)}_(F)).

According to what is illustrated in FIG. 8 , in the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air in the duct 25 is less than the threshold value THR, the third contribution α_(ADAT) with which to operate the shut-off valve 26 is used to update the map used previously to determine the nominal passage section α_(NOM) with which to operate the shut-off valve 26. In particular, the third contribution α_(ADAT) is provided at input to the map together with further quantities that comprise the pressure P_(BURN) of the air being fed to the burner 21, the pressure P_(A) and the temperature T_(A) of the air in the duct 25. The map provides at output the updated value of the air flow rate {dot over (m)}_(A_RPL).

In the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air in the duct 25 is greater than the threshold value THR, the value V_(BAT) is instead provided at input to the map together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the nominal value of the air flow rate {dot over (m)}_(A_NOM).

However, the air flow rate {dot over (m)}_(A_RPH) is defined by the sum of the nominal value of the air flow rate {dot over (m)}_(A_NOM) and two further contributions.

In particular, the nominal value of the air flow rate {dot over (m)}_(A_NOM) represents the open-loop contribution and is precisely generated using the experimentally derived control map. The closed-loop contribution {dot over (m)}_(A_ADAT), is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution {dot over (m)}_(A_ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}A and fuel flow rate {dot over (m)}_(F)).

In the case where the sum of the closed-loop contribution α_(CL) and the third contribution α_(ADAT) is greater than a calibratable threshold value THR₂, a breakdown or fault is diagnosed.

In the case where the sum of the closed-loop contribution {dot over (m)}_(A_CL) and the third contribution {dot over (m)}_(A_ADAT) is greater than a calibratable threshold value THR₃, a breakdown or fault is diagnosed.

According to a third variant, the pumping device 24 is regulated by controlling the number N of revolutions while the shut-off valve 26 is produced with the variable/adjustable passage section (in other words, the shut-off valve 26 is not of the on/off type). Also in this case, the pressure sensor 38 is provided in the duct 25 downstream of the shut-off valve 26 to detect the pressure P_(BURN) of the air being fed to the burner 21.

The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N) that are obtained by operating the pumping device 24, the shut-off valve 26, the pumping device 30 and the injector 27.

According to what is illustrated schematically in FIG. 9 , the objective air flow rate {dot over (m)}_(A_OBJ) is provided at input to a map (typically provided by the manufacturer of the shut-off valve 26) together with further quantities that comprise the pressure P_(A) and the temperature T_(A) of the air provided by the sensor 33 and the pressure P_(BURN) of the air being fed to the burner 21 provided by the sensor 38. The map provides at output the nominal passage section α_(NOM) with which to operate the shut-off valve 26.

The actual passage section α_(OBJ) with which to operate the shut-off valve 26 is, however, defined by the sum of the nominal passage section α_(NOM) and any two further contributions.

In particular, the nominal passage section α_(NOM) with which to operate the shut-off valve 26 represents the open-loop contribution and is precisely generated using the experimentally derived control map. In the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air is less than a threshold value THR, the closed-loop contribution α_(CL) is provided by means of a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution α_(ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}_(A) and fuel flow rate {dot over (m)}_(F)).

In addition, the objective air flow rate {dot over (m)}A_OBJ is also provided at input to a map (typically provided by the manufacturer of the pumping device 24) together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the objective air pressure P_(A_OBJ) in the duct 25 (which is determined depending on the objective air flow rate {dot over (m)}_(A_OBJ) and on the pressure P_(BURN) of the air being fed to the burner 21). The map provides at output the nominal number N_(NOM) of revolutions with which to operate the pumping device 24.

The actual number N of revolutions with which to operate the pumping device 24 is, however, defined by the sum of the nominal number N_(NOM) of revolutions and any three further contributions.

In particular, the nominal number N_(NOM) of revolutions with which to operate the pumping device 24 represents the open-loop contribution and is precisely generated using the experimentally derived control map. The closed-loop contribution N_(CL) is provided by means of a PID₁ controller which tries to zero an error in the air pressure, namely, a difference between the objective air pressure P_(A_OBJ) in the duct 25 (which is determined depending on the objective air flow rate {dot over (m)}_(A_OBJ) and on the pressure P_(BURN) of the air being fed to the burner 21) and the actual pressure value P_(A) of the air measured by the sensor 33.

In addition, in the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air is greater than a threshold value THR, a further closed-loop contribution N_(CL2) is provided by means of a PID₂ controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution N_(ADAT) is also determined depending on the sum of the integral action of the PID₁ controller and of the PID₂ controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}_(A) and fuel flow rate {dot over (m)}_(F)).

In other words, regulation of the air flow rate {dot over (m)}_(A) is controlled depending on the ratio between the pressure P_(BURN) of the air being fed to the burner 21 (downstream of the shut-off valve 26) and on the pressure P_(A) of the air (upstream of the shut-off valve 26). When the said ratio is less than the threshold value THR, to control the air flow rate {dot over (m)}_(A), the opening of the shut-off valve 26 is operated; since said ratio is greater than the threshold value THR, to control the air flow rate {dot over (m)}_(A), the pumping device 24 is operated and the shut-off valve 26 is substantially fully open.

According to what is illustrated in FIG. 10 , in the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air in the duct 25 is greater than the threshold value THR, the third contribution N_(ADAT) with which to operate the pumping device 24 is used to update the map used previously to determine the nominal number N_(NOM) of revolutions. In particular, the third contribution N_(ADAT) is provided at input to the map together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the updated value of the air flow rate {dot over (m)}_(A_RPH).

On the other hand, in the case where the ratio between the pressure P_(BURN) of the air being fed to the burner 21 and the pressure P_(A) of the air in the duct 25 is less than the threshold value THR, the third contribution α_(ADAT) with which to operate the shut-off valve 26 is used to update the map used previously to determine the nominal passage section α_(NOM) with which to operate the shut-off valve 26. In particular, the third contribution α_(ADAT) is provided at input to the map together with further quantities that comprise the pressure P_(BURN) of the air being fed to the burner 21, the pressure P_(A) and the temperature T_(A) of the air in the duct 25. The map provides at output the updated value of the air flow rate {dot over (m)}_(A_RPL).

In the case where the sum of the closed-loop contribution N_(CL) and the third contribution N_(ADAT) is greater than a calibratable threshold value THR₁, a breakdown or fault is diagnosed.

In the case where the sum of the closed-loop contribution α_(CL) and the third contribution α_(ADAT) is greater than a calibratable threshold value THR₂, a breakdown or fault is diagnosed.

According to a fourth variant schematically illustrated in FIG. 13 , the pumping device 24 is regulated by controlling the number N of revolutions while the shut-off valve 26 is of the on/off type.

The electronic control unit ECU is designed to determine the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N) that are obtained by operating the pumping device 24, the pumping device 30 and the injector 27.

According to what is illustrated schematically in FIG. 11 , the objective air flow rate {dot over (m)}_(A_OBJ) is also provided at input to a map (typically provided by the manufacturer of the pumping device 24) together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the nominal number N_(NOM) of revolutions with which to operate the pumping device 24.

The actual number N of revolutions with which to operate the pumping device 24 is, however, defined by the sum of the nominal number N_(NOM) of revolutions and two further contributions.

In particular, the nominal number N_(NOM) of revolutions with which to operate the pumping device 24 represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N_(CL) is provided by means of a PID controller which tries to zero an error in the air flow rate, namely, a difference between the objective air flow rate {dot over (m)}_(A_OBJ) and the air flow rate {dot over (m)}_(A).

In addition, according to what is illustrated in FIG. 13 , the air flow rate {dot over (m)}_(A) is calculated by subtracting the total air flow rate {dot over (m)}_(TOT) detected by the mass air flow sensor 9 from the air flow rate {dot over (m)}_(ICE) fed to the internal combustion engine 1. The air flow rate {dot over (m)}_(ICE) fed to the internal combustion engine 1 is determined, for example, by the method to determine the mass of air trapped in each cylinder of an internal combustion engine described in the patent applications EP3650678 and EP3739192A, which are incorporated herein for reference.

The third contribution N_(ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}_(A) and fuel flow rate {dot over (m)}_(F)).

According to what is illustrated in FIG. 12 , the third contribution N_(ADAT) with which to operate the pumping device 24 is then used to update the map used previously to determine the nominal number N_(NOM) of revolutions. In particular, the difference between the actual number N of revolutions with which to operate the pumping device 24 and the third contribution N_(ADAT) is provided at input to the map together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the updated value of the air flow rate {dot over (m)}_(A).

In the case where the sum of the closed-loop contribution N_(CL) and the third contribution N_(ADAT) is greater than a calibratable threshold value THR₁, a breakdown or fault is diagnosed.

According to a fifth and final variant illustrated schematically in FIG. 14 , the pumping device 24 is regulated by controlling the number N of revolutions while the shut-off valve 26 is of the on/off type. A mass air flow sensor 39 (better known as Air Flow Meter) is also arranged along the duct 25, interposed between the pumping device 24 and the shut-off valve 26.

According to a further embodiment (not illustrated), the mass air flow sensor is arranged along the duct 25 upstream of the pumping device 24.

The electronic control unit ECU is therefore designed to determine the objective air flow rate {dot over (m)}_(A_OBJ) and the nominal fuel flow rate {dot over (m)}_(F_N) that are obtained by operating the pumping device 24, the pumping device 30 and the injector 27.

According to what is illustrated schematically in FIG. 11 , the objective air flow rate {dot over (m)}_(A_OBJ) is also provided at input to a map (typically provided by the manufacturer of the pumping device 24) together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the nominal number N_(NOM) of revolutions with which to operate the pumping device 24.

The actual number N of revolutions with which to operate the pumping device 24 is, however, defined by the sum of the nominal number N_(NOM) of revolutions and two further contributions.

In particular, the nominal number N_(NOM) of revolutions with which to operate the pumping device 24 represents the open-loop contribution and is precisely generated using the experimentally derived control map; while the closed-loop contribution N_(CL) is provided by means of a PID controller which tries to zero an error in the air flow rate, namely, a difference between the objective air flow rate {dot over (m)}_(A_OBJ) and the air flow rate {dot over (m)}_(A) detected by the mass air flow sensor 39.

The third contribution N_(ADAT) is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}_(A) and fuel flow rate {dot over (m)}_(F)).

According to what is illustrated in FIG. 12 , the third contribution N_(ADAT) with which to operate the pumping device 24 is then used to update the map used previously to determine the nominal number N_(NOM) of revolutions. In particular, the third contribution N_(ADAT) is provided at input to the map together with further quantities that comprise the ambient pressure P_(ATM) and the ambient temperature T_(ATM) provided by the sensor 37 and the pressure P_(A) of the air in the duct 25 provided by the sensor 33. The map provides at output the updated value of the air flow rate {dot over (m)}_(A).

In the case where the sum of the closed-loop contribution N_(CL) and the third contribution N_(ADAT) is greater than a calibratable threshold value THR₁, a breakdown or fault is diagnosed.

According to what is schematically illustrated in FIG. 5 , once the electronic control unit ECU has determined the actual number N of revolutions with which to operate the pumping device 24 to obtain the objective air flow rate {dot over (m)}_(A_OBJ), the nominal fuel flow rate {dot over (m)}_(F_N) is calculated.

The nominal fuel flow rate {dot over (m)}_(F_N) is determined by the following formula:

${\overset{.}{m}}_{{FUEL} - N} = \frac{{\overset{.}{m}}_{A}}{\left( {\frac{A}{F_{STEC}}*\lambda_{OBJ}} \right)}$

{dot over (m)}_(FUEL-N) nominal fuel flow rate {dot over (m)}_(A) estimated air flow rate A/F_(STEC) stoichiometric air and fuel ratio λ_(OBJ) desired/objective value of the air/fuel ratio.

The estimated air flow rate {dot over (m)}_(A) is determined according to the method illustrated in FIG. 6 and described in the preceding disclosure.

The objective fuel flow rate {dot over (m)}_(F_OBJ) is, however, defined by the sum of the nominal fuel flow rate {dot over (m)}_(FN) and two further contributions.

In particular, the nominal fuel flow rate {dot over (m)}_(F_N) represents the open-loop contribution and is precisely generated using the formula described previously; while the closed-loop contribution of the fuel flow rate is provided by a PID controller which tries to zero an error in the air/fuel ratio, namely, a difference between the objective value λ_(OBJ) of the air/fuel ratio and the actual value λ of the air/fuel ratio measured by the UHEGO or UEGO type linear oxygen sensor 18, 18*.

The third contribution {dot over (m)}_(F_ADAT) of the fuel flow rate is also determined depending on the integral action of the PID controller under stationary conditions (i.e., with stationary air flow rate {dot over (m)}_(A) and fuel flow rate {dot over (m)}_(F)).

In the case where the sum of the closed-loop contribution {dot over (m)}_(F_CL) and the third contribution {dot over (m)}_(F_ADAT) is greater than a calibratable threshold value THR₄, a breakdown or fault is diagnosed.

In the case of a fault of the mass air flow sensor 9 or 39, the air flow rate {dot over (m)}_(A) is calculated by means of a map depending on the ambient pressure P_(ATM), on the ambient temperature T_(ATM) and on the pressure P_(A) of the air entering the burner 21, the actual number N of revolutions with which to operate the pumping device 24, and the further adaptive contribution N_(ADAT) of the number of revolutions with which to operate the pumping device 24.

It is clear that the strategies described in the previous disclosure to control and adapt the objective fuel flow rate {dot over (m)}_(F_OBJ) and the air flow rate {dot over (m)}_(A) may be used with any layout of the exhaust system 2 (regardless of the position of the linear oxygen sensor 18, 18*).

It is also clear that the previous disclosure may also find advantageous application in the case where the linear oxygen sensor 18, 18*, 18** is replaced by a lambda sensor suited to provide a binary on/off type output (indicating whether the exhaust gases titer is above or below the stoichiometric value).

In particular, the strategies described in the previous disclosure may also find advantageous application in the case of a linear oxygen sensor 18** housed along the outlet duct 35.

LIST OF REFERENCE NUMBERS

-   1 internal combustion engine -   2 exhaust system -   3 cylinders -   4 intake manifold -   5 exhaust manifold -   6 intake duct -   7 air filter -   8 throttle valve -   9 mass air flow sensor -   10 exhaust duct -   11 turbocompressor -   12 turbine -   13 compressor -   14 after-treatment system -   15 precatalytic converter -   16 particulate filter -   17 catalytic converter -   18 UEHO linear sensor or HEGO switching -   19 lambda sensor -   20 lambda sensor -   21 burner -   22 combustion chamber -   23 air feeding circuit -   24 pumping device -   25 duct -   26 shut-off valve -   27 injector -   28 spark plug -   29 fuel feeding circuit -   30 pumping device -   31 duct -   32 control system -   33 sensor P, T -   34 sensor P, T -   35 outlet duct * -   36 sensor P, T -   37 sensor P, T -   38 pressure sensor -   39 mass air flow sensor 

1. A method to control an internal combustion engine (1) provided with an exhaust system (2) for the exhaust gases of a motor vehicle having an exhaust duct (10) and an exhaust gas after-treatment system (14) comprising at least one catalytic converter (15, 17) arranged along the exhaust duct (10); and an oxygen sensor (18, 18*, 18**), preferably a linear one, to detect the air/fuel ratio of the exhaust gases providing an output that indicates the content of oxygen in the exhaust gases; and a burner (21), which is suited to introduce exhaust gases into the exhaust duct (10) so as to speed up the heating of said at least one catalytic converter (15, 17), wherein inside the burner (21) there is defined a combustion chamber (22), which receives fresh air through an air feeding device (23), which is provided with a pumping device (24) feeding air, and fuel from an injector (27), which is designed to inject fuel into the combustion chamber (22), and a spark plug (28) coupled to the burner (21) so as to ignite the mixture present inside the combustion chamber (22); the method comprises the following steps: calculating the thermal power (P_(OBJ)) needed to reach the nominal operating temperature of said at least one catalytic converter (15, 17) obtained with an objective value (λ_(OBJ)) of the air/fuel ratio; and determining both the objective fuel flow rate ({dot over (m)}_(F_OBJ)) and the objective air flow rate ({dot over (m)}_(A_OBJ)) to be fed to the burner (21) in order to obtain the thermal power (P_(OBJ)) needed to reach the nominal operating temperature of said at least one catalytic converter (15, 17).
 2. The method according to claim 1 and comprising the further steps of: determining the nominal number (N_(NOM)) of revolutions with which to operate the pumping device (24) depending on the objective air flow rate ({dot over (m)}_(A_OBJ)), on the ambient pressure (P_(ATM)), on the ambient temperature (T_(ATM)) and on the objective pressure (P_(A_OBJ)) of the air flowing into a shut-off valve (26) that regulates a duct (25) located downstream of the pumping device (24); determining a closed-loop contribution (N_(CL)) of the number of revolutions with which to operate the pumping device (24) by means of a PID controller, which tries to zero a difference between the objective value (λ_(OBJ)) of the air/fuel ratio and the actual value (λ) of the air/fuel ratio measured by the oxygen sensor (18, 18*, 18**); determining a further contribution (N_(ADAT)) of the number of revolutions with which to operate the pumping device (24) depending on the integral action of the PID controller under stationary conditions; determining the actual number (N) of revolutions with which to operate the pumping device (24) by means of the sum of the nominal number (N_(NOM)) of revolutions, of the closed-loop contribution (N_(CL)) of the number of revolutions with which to operate the pumping device (24) and of the further contribution (N_(ADAT)) of the number of revolutions with which to operate the pumping device (24).
 3. The method according to claim 2, wherein the step of determining the actual number (N) of revolution comprises: determining a first closed-loop contribution (N_(CL1)) by means of a first PID controller (PID₁), which tries to zero an error in the air pressure, namely a difference between the objective air pressure (P_(A_OBJ)) and the actual value (P_(A)) of the air pressure; determining a second closed-loop contribution (N_(CL2)) by means of a second PID controller (PID₂), which tries to zero an error in the air/fuel ratio, namely a difference between the objective value (λ_(OBJ)) of the air/fuel ratio and the actual value (λ) of the air/fuel ratio; and calculating a further contribution (N_(ADAT)) depending on the sum of the integral action of the first PID controller (PID₁) and of the second PID controller (PID₂) under stationary conditions; adding the nominal number (N_(NOM)) of revolutions, the first closed-loop contribution (N_(CL1)), the second closed-loop contribution (N_(CL2)) and the further contribution (N_(ADAT)) of the number of revolutions with which to control the pumping device (24).
 4. The method according to claim 2 and comprising the further step of signalling a fault in case the sum of the first closed-loop contribution (N_(CL1)), of the second closed-loop contribution (N_(CL2)) and of the further contribution (N_(ADAT)) of the number of revolutions with which to operate the pumping device (24) exceeds a predetermined threshold value (THR₁).
 5. The method according to claim 1, wherein the value of the estimated air flow rate ({dot over (m)}_(A)) is calculated by means of the difference between the actual number (N) of revolutions and the further contribution (N_(ADAT)) of the number of revolutions with which to operate the pumping device (24) and by means of the quantities comprising the ambient pressure (P_(ATM)), the ambient temperature (T_(ATM)) and the pressure (P_(A)) of the air in a duct (25) downstream of the pumping device (24).
 6. The method according to claim 1, wherein the estimated air flow rate ({dot over (m)}_(A)) is calculated by means of a compressor model, which is a function of the ambient pressure (P=4), of the ambient temperature (T_(ATM)) and of the objective pressure (P_(A_OBJ)) of the air flowing into the shut-off valve (26) as well as of the supply voltage value.
 7. The method according to claim 6 and comprising the further steps of: calculating a further closed-loop contribution ({dot over (m)}_(A_CL)) by means of a PID controller, which tries to zero a difference between the objective value (λ_(OBJ)) of the air/fuel ratio and the actual value (λ) of the air/fuel ratio measured by the oxygen sensor 18, 18*, 18**); determining a further contribution ({dot over (m)}_(A_ADAT)) depending on the integral action of the PID controller under stationary conditions; and determining the estimate of the air flow rate ({dot over (m)}_(A)) by means of the sum of the nominal value of the air flow rate ({dot over (m)}_(A_NOM)), of the closed-loop contribution ({dot over (m)}_(A_CL)) and of the further contribution ({dot over (m)}_(A_ADAT)).
 8. The method according to claim 1, wherein the air feeding circuit (23) comprises a shut-off valve (26), which is arranged downstream of the pumping device (24) and whose passage section is adjustable; the method comprises the further steps of: determining the nominal passage section (α_(NOM)) with which to operate the shut-off valve (26) depending on the objective air flow rate ({dot over (m)}_(A_OBJ)), on the air pressure (P_(BURN)) downstream of the shut-off valve (26), on the air temperature (T_(A)) and on pressure (P_(A)) of the air flowing into the shut-off valve (26); determining a closed-loop contribution (α_(CL)) of the passage section with which to operate the shut-off valve (26) by means of a PID controller, which tries to zero a difference between the objective value (λ_(OBJ)) of the air/fuel ratio and the actual value (A) of the air/fuel ratio measured by the oxygen sensor (18, 18*, 18**); determining a further contribution (α_(ADAT)) of the passage section with which to operate the shut-off valve (26) depending on the integral action of the PID controller under stationary conditions; determining the actual passage section (α_(OBJ)) with which to operate the shut-off valve (26) by means of the sum of the nominal passage section (α_(NOM)), of the closed-loop contribution (α_(CL)) and of the further contribution (α_(ADAT)) of the passage section with which to operate the shut-off valve (26).
 9. The method according to claim 8 and comprising the further step of calculating the estimated air flow rate ({dot over (m)}_(A)) depending on a flowing model of the air flowing through the shut-off valve (26), of a measured value of the passage section, of the further contribution (α_(ADAT)) of the passage section with which to operate the shut-off valve (26), of the pressure (P_(BURN)) of the air flowing into the burner (21) and of the pressure (P_(A)) of the air flowing into the shut-off valve (26).
 10. The method according to claim 1 and comprising the further step of determining the nominal fuel flow rate ({dot over (m)}_(FUEL_N)) by means of the following formula: ${\overset{.}{m}}_{{FUEL} - N} = \frac{{\overset{.}{m}}_{A}}{\left( {\frac{A}{F_{STEC}}*\lambda_{OBJ}} \right)}$ {dot over (m)}_(FUEL-N) nominal fuel flow rate; {dot over (m)}_(A) estimated air flow rate; A/F_(STEC) stoichiometric air and fuel ratio; Λ_(OBJ) objective value of the air/fuel ratio.
 11. The method according to claim 10 and comprising the further steps of: determining a closed-loop contribution ({dot over (m)}_(F_CL)) of the fuel flow rate by means of a PID controller, which tries to zero a difference between the objective value (λ_(OBJ)) of the air/fuel ratio and the actual value (λ) of the air/fuel ratio measured by the oxygen sensor (18, 18*, 18**); determining a further contribution ({dot over (m)}_(F_ADAT)) of the fuel flow rate depending on the integral action of the PID controller under stationary conditions; and determining the objective fuel flow rate ({dot over (m)}_(F_OBJ)) by means of the sum of the nominal fuel flow rate ({dot over (m)}_(FUEL_N)), of the closed-loop contribution ({dot over (m)}_(CL)) of the fuel flow rate and of the further contribution ({dot over (m)}_(F_ADAT)) of the fuel flow rate.
 12. The method according to claim 11 and comprising the further step of signalling a fault in case the sum of the closed-loop contribution ({dot over (m)}_(F_CL)) and of the further contribution ({dot over (m)}_(F_ADAT)) of the fuel flow rate exceeds a predetermined threshold value. 